Production of a prescribed level of protective antibodies following immunization with toxoid vaccines containing a Diphtheria component is required for release of the vaccine lot. Currently, a second animal test is employed to evaluate the efficacy of the animal response to the injected vaccine. This research has focused on replacing this second animal test with an in-vitro cell test. Results of the six laboratory collaborative study were presented in December, 1997 at the FDA Science Forum. These data were also reviewed in several international meetings, and plans to develop and implement a collaborative study have been discussed. A supply of well-characterized Diphtheria Toxin will be necessary for any collaborative study. Because of limited personnel and financial resources, no additional laboratory studies were performed this year.